Anaerobic methane oxidation inducing carbonate precipitation at abiogenic methane seeps in the Tuscan archipelago (Italy)
Fig 7
Isotope compositions of seep carbonates.
(A) Cross plot of δ13C and δ18O from carbonates micro-drilled from several different cemented fragments. (B) The same δ13C values as in (A) plotted against the percentage of aragonite relative to all carbonate phases. Different aragonite contents are due to variable contribution of biogenic high-Mg calcite (probably from bryozoans). The isotopic composition of the pure aragonite cement can be extrapolated with the regression line. (C) The same for δ18O values. The regression line shows practically no slope between samples rich in Mg-calcite and samples rich in aragonite.